Simple synthesis of uniformly small gold nanoparticles for sensitivity enhancement in colorimetric detection of Pb2+ by improving nanoparticle reactivity and stability

Abstract

We first synthesized high-quality gold nanoparticles (Au NPs) with size ranging from 5.5 to 17.8 nm in high yield via a robust, one-step seeded growth method using Tris-base (TB). It was found that the narrow distribution in size and shape of the as-prepared Au NPs was affected by reaction temperature and pH value of the reaction media. The sizes of these small Au NPs could be finely controlled by varying the gold precursor and/or seed amount according to an established relationship between the NP diameter and the particle number of the seeds (or the mass of the gold precursor in some cases). Due to their highly colloidal stability, TB-stabilized Au NPs (TB-Au NPs) could be directly used for the detection of Pb²⁺. Pb²⁺ can be determined in a large linear range of 0.1 nM to 5 μM with a high determination coefficient, good repeatability (10 times at least) and high selectivity (1 : 200) by our 2-mercaptoethanol (2-ME)/S₂O₃²⁻–TB-Au_m NP sensors (m represents the size of Au NPs, m = 5.5, 10, and 15 nm). Moreover, the limit of detection (LOD) of the 2-ME/S₂O₃²⁻–TB-Au_5.5 NP sensor for Pb²⁺ could be as low as 0.1 nM, which, to the best of our knowledge, is the lowest one obtained by a colorimetric method thus far. Furthermore, our 2-ME/S₂O₃²⁻–TB-Au_5.5 NP sensor could also detect Pb²⁺ in real soil extracts with satisfactory recovery. Thus, the 2-ME/S₂O₃²⁻–TB-Au_5.5 NP sensor could be applied for the determination of Pb²⁺ in real samples from complicated natural environments.